Process for catalytic conversion of hydrocarbons into aromatic compounds with a catalyst containing silicon

ABSTRACT

PCT No. PCT/FR96/00919 Sec. 371 Date Dec. 15, 1997 Sec. 102(e) Date Dec. 15, 1997 PCT Filed Jun. 14, 1996 PCT Pub. No. WO97/00306 PCT Pub. Date Jan. 3, 1997A process for converting hydrocarbons into aromatic compounds, which entails contacting a composition containing hydrocarbons with a catalyst under temperature and pressure conditions to produce the aromatic compounds, the catalyst containing a matrix of  eta  transition alumina and/or  gamma  transition alumina. The catalyst contains 0.001 to 2 wt % of silicon, 0.1 to 15 wt % of at least one platinum group metal, and 0.005 to 10 wt % of at least one promoter metal. The promoter metals may be tin, germanium, indium, gallium, thallium, antimony, lead, rhenium, manganese, chromium, molybdenium or tungsten. The catalyst may also contain a doping metal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a process for catalytic conversion ofhydrocarbons into aromatic compounds, which can be used in particularfor the reforming of gasolines and the production of aromatics.

More precisely, it concerns a process of this type using as catalyst amulti-functional catalyst with an alumina matrix.

2. Description of the Background

Catalytic reforming is a process which makes it possible to improve theoctane number of the oil fractions and in particular of the heavypetroleum from distillation by conversion of n-paraffins and naphthenesinto aromatic hydrocarbons.

The operation of catalytic reforming thus consists on the one hand oftransforming C₇ -C₁₀ n-paraffins into aromatics and light paraffins andon the other hand C₇ -C₁₀ naphthenes into aromatics and light paraffins.These reactions are illustrated in particular by the conversion bydehydrogenation of cyclohexanes and the dehydroisomerization ofalkylcyclopentanes to yield aromatics, methylcyclohexane yielding forexample toluene, and also by conversion by cyclization of n-paraffinsinto aromatics, n-heptane for example yielding toluene.

During catalytic reforming, cracking reactions also take place of heavyn-paraffins into light paraffins leading in particular to C₁ -C₄products essentially of propane and isobutane: these reactions aredetrimental to the yield of reformed product.

Finally, there is also the formation of coke through condensation ofaromatic nuclei forming a solid product, rich in carbon which isdeposited on the catalyst.

The reforming catalysts are very sensitive, apart from coke, to variouspoisons which can reduce their activity: in particular sulphur,nitrogen, metals and water.

By being deposited on the surface of the catalyst, the coke brings abouta loss in activity with time which leads to higher operatingtemperatures, a lower yield of reformed products, and a higher gasyield.

Because of this and considering the regeneration of the catalyst, thecatalytic reforming process can be put into operation in two differentways: in a semi-regenerating or cyclic manner and in a continuousmanner. In the first case, the process is carried out with a fixed bed,in the second with a mobile bed.

In the semi-regenerating process, to compensate for the loss of activityof the catalyst, the temperature is raised progressively and then theinstallation is stopped in order to carry out the regeneration of thecatalyst by eliminating the coke. In cyclic reforming which in fact is avariation of the semi-regenerating process, the installation comprisesseveral reactors in series and each is closed down in turn, the cokedeposits are eliminated from the catalyst out of action and the catalystregenerated while the other reactors continue to operate.

In continuous reforming, the reactors put into operation are moving-bedreactors operating at low pressure (less than 15 bars), which makes itpossible to raise considerably the yields of reformed products andhydrogen by encouraging aromatization reactions instead of cracking, buton the other hand the formation of coke is greatly accelerated. Thecatalyst passes through the reactors then a regenerating action.

The processes for production of aromatics involve conversion reactionsof the paraffinic and naphthenic hydrocarbons into aromatic compounds.

In these processes of conversion of hydrocarbons, bi-functionalcatalysts are generally used containing, for example, platinum and asupport of chlorinated alumina, which associate the acidic function ofthe chlorinated alumina necessary for the reactions of isomerization ofcyclopentanic naphthenes and the cyclization of paraffins with thedehydrogenating function of the platinum necessary for thedehydrogenation reactions. Catalysts of this type also including anothermetal such as rhenium, tin or lead have been described in U.S. Pat. No.3,700,588 and U.S. Pat. No. 3,415,737.

As it can be seen above, the catalytic reforming processes can beoperated either by using a fixed bed or a mobile bed of catalyst.

In each case, the catalyst undergoes a regenerating treatment operatingat high temperature and in the presence of steam, which consists amongother things of burning off the coke deposited on the catalyst.Unfortunately, these treatment conditions favour degradation of thecatalyst. It is thus important to try to raise the resistance of thecatalyst under these conditions.

Generally the catalyst is presented in the form of extrusions or ballsof a sufficient size to let the reagents and gaseous products passrelatively easily. Wear of the catalyst results, in particular throughfriction in processes with mobile beds, which provokes the formation ofdusts and finer grains. These very fine grains perturb the gaseous flowand make it necessary to raise the entry pressure of the reagents andeven, in certain cases, to stop the unit. In mobile bed units, thisprogressive wear also has the consequence of perturbing the circulationof the catalyst and makes it necessary to top up the catalystfrequently.

A catalyst such as a reforming catalyst must thus satisfy a great numberof requirements, certain of which may appear contradictory. Thiscatalyst must first of all provide the greatest activity possibleallowing high yields to be obtained, but this activity must also beconjugated with the greatest selectivity possible, that is to say thatcracking reactions leading to light products containing from 1 to 4carbon atoms must be limited.

In addition, the catalyst must be highly stable vis-a-vis itsdeactivation through coke deposit; the catalyst must also have excellentresistance to degradation when it is submitted to the extreme conditionsexisting in the repeated regenerating operations it has to undergo.

In the case of the continuous reforming process operating for mobile bedreactors and as mentioned above, the catalysts are also submitted tointense and progressive wear through friction, which leads to aconsiderable diminution of their specific surface area and the formationof "smalls" which prejudice the functioning of the installation. Thecatalysts available at present, even if they can fulfill one or severalof these conditions, do not satisfy the whole range of the requirementsmentioned above.

Also, despite the many improvements already made to the bi-functionalcatalysts used, one is still looking for new catalysts offering improvedperformance, not only as far as the yield of conversion reactions isconcerned, but also the lifespan of the catalyst.

SUMMARY OF THE INVENTION

The present invention concerns precisely a process for conversion ofhydrocarbons using a multi-functional catalyst which presents improvedcatalytic performance and an extended lifespan in reforming reactionsand production of aromatics.

According to the invention, the process for conversion of hydrocarbonsinto aromatic components consists of putting a load of said hydrocarbonsinto contact with a catalyst under the temperature and pressureconditions appropriate for said conversion, and it is characterized inthat the catalyst comprises:

a matrix constituted of 0 to 100% by weight of η transition alumina, thecomplement to 100% by weight of the matrix being γ transition alumina,and

compared with the total weight of the catalyst,

from 0.001 to 2% by weight of silicon,

from 0.1 to 15% by weight of at least one halogen chosen from among thegroup formed by fluorine, chlorine, bromine and iodine,

from 0.01 to 2% by weight of at least one noble metal of the platinumgroup,

from 0.005 to 10% by weight of at least one promoter metal chosen fromthe group formed by tin, germanium, indium, gallium, thallium, antimony,lead, rhenium, manganese, chromium, molybdenum and tungsten, saidcatalyst having undergone a complementary hydrothermal treatment, at atemperature from 300 to 1000° C., in a gaseous atmosphere containingsteam.

DETAILED DESCRIPTION OF THE INVENTION

In one embodiment of the invention, the catalyst comprises in additionfrom 0.001 to 10% by weight of at least one doping metal chosen from thegroup constituted of the alkali and alkaline-earth metals, thelanthanides, titanium, zirconium, hafnium, cobalt, nickel and zinc.

It is to be noted that in the continuation of this text all the contentsof silicon, halogen, noble metal, promoter metal and doping metal areexpressed in % by weight compared to the total weight of the catalyst,unless indicated to the contrary. Moreover, these content levelscorrespond to the total content of constituent (doping metal, halogen,noble metal or promoter metal) when the constituent comprises severalelements (halogens or metals).

In the invention, the application of a complementary hydrothermaltreatment of the catalyst is very important. In fact, in the catalystsof the invention, it has been noted that the presence of siliconpreserves the matrix in alumina(s) of the catalyst from a loss ofspecific surface area when it is submitted to the regenerationtreatments necessary for its operation in conversion reactions ofhydrocarbons, but the catalyst with silicon has the disadvantage ofproducing a high degree of cracking. In unexpected fashion, theapplicant has noted that severe complementary hydrothermal treatment inthe presence of water applied to this type of catalyst has the effect ofpreserving the loss of specific surface area, while also improvingcatalytic performance (less cracking).

Preferably, this complementary hydrothermal treatment is carried out ina gaseous atmosphere containing not only steam but also a halogen suchas chlorine.

A preferred catalyst of the invention comprises:

a support constituted of a matrix of γ alumina, of η alumina or of amixture of γ alumina and η alumina plus silicon.

at least one halogen,

a catalytic metal ensuring the function of dehydrogenation of thecatalyst, constituted of one or several noble metals of the platinumgroup, and

at least one promoter metal chosen from among the metals cited above.

In the invention the matrix is a base of a hydrated oxide of aluminium.It is known that supports in alumina of the general formula Al₂ O₃ -nH₂O, where n is from 0 to 0.6, which present a specific surface area of150 to 400 m² /gm, can be obtained by controlled dehydration ofamorphous aluminium hydroxides where n has a value of between 1 and 3.The original amorphous hydroxides can exist under several forms and themost common are boehmite (n=1) gibbsite and bayerite (n=3), and they canlead during dehydration treatment to several transition oxides oraluminas such as the forms ρ, γ, η, χ, θ, δ, κ, and α which aredifferentiated essentially by the organization of their crystallinestructure. During thermal treatments, these different forms aresusceptible to evolution between themselves, following a complexrelationship which depends on the operating conditions of the treatment.The a form which presents a specific surface area and acidity which arenearly zero, is the most stable at high temperatures. For reformingcatalysts, the γ form of transition alumina is used most often, becauseof the compromise it offers between its properties of acidity andthermal stability.

In the invention, γ transition alumina or η transition alumina is used,or preferably a mixture of γ transition alumina and η transitionalumina.

η transition alumina can be obtained by roasting bayerite in dry air, atatmospheric pressure, between 250 and 500° C., preferably between 300and 450° C. The specific surface area achieved which depends on thefinal temperature of roasting, is between 300 and 500 m² /gm. The γalumina comes from boehmite through roasting under air at a temperaturebetween 450 and 600° C. The specific surface area of the γ aluminaobtained is between 100 and 300 m² /gm.

These two transition aluminas have crystalline structures which areclose but distinctive. The technique of X-ray diffraction can, inparticular, differentiate between them. Their structures are of thespinel type with faults, and their networks are slightly distant fromcubic symmetry. This quadratic deformation is minimal for the η form andis much clearer for γ alumina whose unit-cell parameters are as follows:a=b=7.95 Å and c=7.79 Å.

According to the invention, when a mixture of γ transition alumina and ηtransition alumina is used, this can comprise from 0.1 to 99% or ratherfrom 1 to 84% by weight of η alumina. Preferably, this mixture comprises3 to 70% by weight, and even better 5 to 50% by weight of η transitionalumina, the complement to reach 100% by weight of the mixture being γtransition alumina.

According to the invention, the alumina matrix is modified by silicon.

The content of silicon of the catalyst is between 0.001 to 2% by weight,preferably 0.01 to 1% by weight.

The halogen or halogens used to acidify the support can represent atotal of 0.1 to 15% by weight, and preferably 0.2 to 10% by weight.Preferably, a single halogen is used, in particular chlorine.

The catalyst also comprises one or several promoter metals which havethe effect of promoting the dehydrogenation activity of the noble metalof the platinum group and of limiting the dispersion loss of the atomsof the noble metal from the support surface, which is partly responsiblefor the deactivation of the catalyst.

The total content of promoter metals is 0.005 to 10% by weight,preferably 0.01 to 1% by weight.

The promoter metals are chosen in function of the method of utilizationof the catalyst.

Thus, when the catalyst is to be used in a fixed bed process, thepromoter metal is chosen preferably from the group constituted byrhenium, manganese, chromium, molybdenum, tungsten, indium and thallium.

When the catalyst is to be used in a mobile bed process, the promotermetal is chosen preferably from the group constituted by tin, germanium,indium, antimony, lead, thallium and gallium.

Among these, rhenium-is preferred for fixed bed processes and tin formobile bed processes, since they produce the best promoter effects onthe activity of the catalyst.

In particular, rhenium increases the stability of the catalyst vis-a-visits deactivation by coke deposits. Thus, preferably, rhenium is used incatalysts for fixed bed units since this added stability makes itpossible to lengthen the reactive cycles between two catalystregenerations.

As far as tin is concerned, this makes it possible to improve theperformance of catalysts when they are used at low pressure. Thisimprovement together with the lower cracking activity of catalysts usingtin permits improved yields of reformed products, above all incontinuous regeneration processes on mobile beds functioning at lowoperating pressure.

The total promoter metal(s) content is from 0.005 to 10% by weight,preferably 0.01 to 1% by weight.

When the catalyst only contains a single promoter metal, for examplerhenium or tin, it is preferably present at 0.005 to 0.9% by weight or,even better, at 0.01 to 0.8% by weight.

The catalyst according to the invention comprises as well at least onenoble metal of the platinum group, at 0.01 to 2% by weight, andpreferably 0.1 to 0.8% by weight.

The noble metals which can be used are platinum, palladium, iridium;platinum is to be preferred.

According to one embodiment of the invention, the catalyst comprises inaddition 0.001 to 10% by weight of at least one doping metal chosen fromthe group constituted by the alkali and alkaline-earth metals,lanthanides, titanium, zirconium, hafnium, cobalt, nickel and zinc.

In this case, the alumina matrix is modified with silicon and one orseveral doping metals.

Preferably, the doping metals belong to just one of the followinggroups:

1) the group of alkali and alkaline-earth metals,

2) the group of lanthanides, and

3) the group comprising titanium, zirconium, hafnium, cobalt, nickel andzinc.

In the case of metals belonging to the first group (alkali andalkaline-earth metals) the total content of doping metal of the catalystis generally 0.001 to 8% by weight.

The alkaline metals used can be lithium, sodium, potassium, rubidium andcaesium; the alkaline-earth metals can be chosen from among beryllium,magnesium, calcium, strontium and barium.

The content of doping metal of the first group is chosen in particulardepending on the reactor in which the catalyst of the invention will beused.

Thus, in the case of a fixed bed reactor, the content of doping metal ofthe catalyst is generally within the range of 0.001 to 0.3%, andpreferably between 0.005 and 0.3% or even better 0.01 and 0.3% byweight.

In the case of a mobile bed reactor, the content of doping metal of thecatalyst is higher, generally from more than 0.3 to 8%, preferably morethan 0.3 to 4% and even better 0.7 to 4% by weight.

Preferably, the doping metal is an alkaline metal such as potassium.

In the case of doping metals belonging to the second group(lanthanides), the total content of doping metal of the catalyst can befrom 0.001 to 10% by weight.

The group of lanthanides or rare earths is comprised of the elements ofthe lanthanum group in the Mendeleev periodic table and whose atomicnumbers are between 57 and 71, for example lanthanum, cerium, neodymiumand praseodymium.

The total content of doping metal of the second group is also chosen inparticular depending on the reactor in which the catalyst will be used.

Thus, it can be preferably between 0.001 to 0.5% and even better 0.01 to0.5% by weight when the catalyst is used in a fixed bed process.Preferably, it is from more than 0.5 to 10%, or even better from morethan 0.5 to 4% by weight when the catalyst is used in a mobile bedprocess.

In the case of doping metals belonging to the third group (Ti, Zr, Hf,Co, Ni, Zn), the total content of doping metal of the catalyst can befrom 0.001 to 10% by weight.

It can also be chosen in function of the reactor in which the catalystis to be used.

Thus, the total content of doping metal of the third group is,preferably, from 0.001 to 0.7% and even better from 0.01 to 0.7% byweight when the catalyst is used in a fixed bed process. Preferably, itis more than 0.7 to 10% and even better more than 0.7 to 4% by weightwhen the catalyst is used in a mobile bed process.

The catalyst of the invention can be prepared by depositing itsdifferent constituents on the alumina matrix. The deposit of eachconstituent can be carried out totally or partially on one or both ofthe two aluminas of the matrix before or after it is formed. Theconstituents can be deposited separately or simultaneously in any orderwhatsoever.

Thus, when a mixture of aluminas is used as matrix, the constituents ofthe catalyst can be deposited simultaneously on the two aluminas or onone of them, preferably on the η alumina before carrying out the mixtureof the two aluminas and forming them.

It is also possible to carry out a partial or total deposit of one orcertain constituents on the two aluminas or one of them before mixingthem, and then carry out the other deposits after mixing of the twoaluminas, either before or after the forming of the mixture. When onedeposits one or several constituents before mixing the two aluminas, itis preferable to carry out the deposit of silicon on the η transitionalumina.

Nonetheless, according to the invention, it is generally preferable tomix the two aluminas before depositing the metallic constituents and thehalogen or halogens.

The invention also concerns a process for preparing the catalyst of theinvention, which comprises the following stages:

a) preparation if required by mixing and then by forming of a matrix inγ transition alumina, in η transition alumina, or in a mixture of ηtransition alumina and γ transition alumina.

b) deposit on at least one of the γ and η transition aluminas of one ofthe following constituents, in the weight percentages given below, whichrefer to the total weight of the catalyst;

from 0.001 to 2% by weight, preferably from 0.01 to 1% by weight, ofsilicon,

from 0.1 to 15%, preferably 0.2 to 10% by weight of at least one halogenchosen from the group constituted by fluorine, chlorine, bromine andiodine,

from 0.01 to 2% of at least one noble metal of the platinum group, and

from 0.005 to 10% by weight of at least one promoter metal chosen fromthe group constituted by tin, germanium, indium, gallium, thallium,antimony, lead, rhenium, manganese, chromium, molybdenum and tungsten,

from 0.001 to 10% by weight if required of at least one doping metalchosen from the group constituted by the alkali and alkaline-earthmetals, lanthanides, titanium, zirconium, hafnium, cobalt, nickel andzinc.

Stages a) and b) can be carried out in any order whatsoever and thedeposits of stage b) can be only partly carried out before stage a) andcan be carried out in any order whatsoever; and

c) complementary hydrothermal treatment of the catalyst obtained afterstages a) and b), at a temperature between 300 and 1000° C., in agaseous atmosphere containing steam.

In a preferred embodiment of this process, first of all a support isprepared formed from the matrix of alumina and silicon, and then onedeposits on this the doping metal or metals, the promoter metal ormetals, the halogen or halogens, and the noble metal or metals of theplatinum group.

In this case, silicon can be deposited on the alumina or the mixture ofaluminas, before or after forming.

Preferably, the silicon is deposited after the forming of the aluminamatrix.

The deposit of the different constituents of the catalyst can be carriedout by classical techniques, in liquid or gaseous phase, starting fromthe appropriate precursor components. When the deposit is made on thealumina matrix which is already formed, the techniques employed can forexample be dry impregnation, impregnation through excess solution orionic exchange. This operation is followed if necessary by drying androasting at a temperature between 300 and 900° C., preferably in thepresence of oxygen.

Thus, the silicon can be deposited from components such as the alkyltetraorthosilicates, the silicon alkoxides, the quaternary ammoniumsilicates, the silanes, the disilanes, the silicones, the siloxanes, thesilicon halides, the halogenosilicates and silicon in the form ofmicro-balls of colloidal silica. In the case where the precursor ofsilicon is a fluorosilicate, this can be expressed by the formulaM_(2/x) SiF₆, where M is a metallic or non-metallic cation with valencyx, chosen from among the following cations: NH₄ ⁺, ammonium alkyls, K⁺,Na⁺, Li⁺, Ba²⁺, Mg²⁺, Cd²⁺, Cu⁺, Cu²⁺, Ca²⁺, Cs⁺, Fe²⁺, Co²⁺, Pb²⁺,Mn²⁺, Rb⁺, Ag⁺, Sr²⁺, Zn²⁺, Tl⁺ and H⁺.

When the silicon is deposited after the forming of the alumina matrix,this deposit is preferably carried out by impregnation in a water mediumby using an excess of aqueous solution of the precursor. Then theimpregnation solvent is eliminated, for example by drying and airroasting is carried out, at a temperature for example between 300 and900° C.

The deposit of the doping metal or metals of the first group chosen fromamong the alkali and alkaline-earth metals can be carried out by anytechnique whatsoever and can take place at any stage of the preparationprocess of the catalyst. When this deposit is made after the forming ofthe matrix of alumina, it is preferable to use impregnation in anaqueous medium by excess of solution, followed by drying to eliminatethe impregnation solvent and roasting in air at a temperature betweenfor example 300 and 900° C.

The precursor components used can be for example salts of the alkali andalkaline-earth metals such as halides, nitrates, carbonates, acetates,sulphates, cyanides and oxalates.

The deposit of doping metal or metals of the second group (lanthanides)can be carried out using any technique known to the state of the art,and can take place at any moment of the preparation of the catalyst. Forexample, in the case where this element of the group of the lanthanidesor rare earths is deposited after the forming of the alumina or aluminascontaining other metals if required, one can use dry impregnation,impregnation through excess of solution or ionic exchange. On a matrixwhich has already been formed, a preferred method for the introductionof this additional element is impregnation in an aqueous medium by usingan excess of solution. In order to eliminate the impregnation solvent,this impregnation is followed by drying and roasting in air at atemperature between, for example, 300 and 900° C.

The precursor components can be, for example, halides, nitrates,carbonates, acetates, sulphates or oxalates of said elements.

The deposit of doping metal or metals of the third group constituted bytitanium, zirconium, hafnium, cobalt, nickel and zinc on the matrix ofthe catalyst used in the present invention, can be carried out accordingto all the state of the art techniques, and can occur at any momentduring the preparation of the catalyst. For example, in the case wherethis element is deposited after the forming of the alumina or aluminascontaining if required other metals, one can use dry impregnation,impregnation through excess solution, or ionic exchange. On a matrixwhich is already formed, a preferred method for introducing thisadditional element is impregnation in an aqueous medium by using anexcess of solution. In order to eliminate the impregnation solvent, thisimpregnation is followed by drying and roasting in air at a temperatureof between, for example, 300 and 900° C.

The deposits of silicon and at least one element chosen from the groupconstituted by titanium, zirconium, hafnium, cobalt, nickel and zinc canbe carried out independently from each other, either on a transitionalumina or on the non-formed matrix, said matrix comprising between 0and 99% by weight of η transition alumina and the complement up to 100%of γ transition alumina, or yet again on the preformed matrix, thelatter being the preferred method.

The deposit of a noble metal or metals of the platinum group can also becarried out by classical techniques, in particular impregnation from anaqueous solution or not containing a salt or compound of the noblemetal. As an example of salts or compounds which can be used, one cancite chloroplatinic acid, ammoniated compounds, ammoniumchloroplatinate, platinum dicarbonyl dichloride, hexahydroxyplatinicacid, palladium chloride and palladium nitrate.

In the case of platinum, the ammoniated compounds can for example be thesalts of platinum IV hexamines of formula Pt(NH₃)₆ X₄, the salts ofplatinum IV halogenopentamines of formula (PtX(NH₃)₅)X₃, the salts ofplatinum tetrahalogenodiamines of formula PtX₄ (NH₃)₂ X, the complexesof platinum with halogens-polyketones and the halogen compounds offormula H (Pt(aca)₂ X) in which the element X is a halogen chosen fromthe group comprising chorine, fluorine, bromine and iodine, andpreferably chlorine, and the group aca represents the rest of theformula C₅ H₇ O₂ derived from acetylacetone. The introduction of thenoble metal of the platinum group is preferably carried out byimpregnation with the aid of an aqueous or organic solution of one ofthe organometallic compounds cited above. Among the organic solventswhich can be used, one can cite the paraffinic, naphthenic or aromatichydrocarbons, and the organic halogen compounds with for example 1 to 12carbon atoms per molecule. One can cite for example n-heptane,methylcyclohexane, toluene and chloroform. Mixtures of solvents can alsobe used.

After introduction of the noble metal, drying and roasting is preferablycarried out, for example at a temperature of between 400 and 700° C.

The deposit of a noble metal or noble metals of the platinum group canoccur at any moment during the preparation of the catalyst. It can becarried out in isolation or simultaneously with the deposit of otherconstituents, for example the promoter metal or metals. In the lattercase, for impregnation, a solution can be used containing all theconstituents to be introduced simultaneously.

The deposit of the promoter metal or metals can also be carried out byclassical techniques beginning from precursor compounds such as thehalogens, nitrates, acetates, tartrates, citrates, carbonates and theoxalates of these metals. Any other salt or oxide of these metals whichis soluble in water, acids, or in another appropriate solvent, is alsosuitable as a precursor. As examples of such precursors, one can citethe rhenates, chromates, molybdates and tungstates. One can alsointroduce the promoter metal or metals through mixture of an aqueoussolution of their precursor compound(s) with the alumina or aluminasbefore forming, followed by roasting in air at a temperature between 400and 900° C.

The introduction of the promoter metal or metals can also be carried outwith the aid of a solution of an organometallic compound of said metalsin an organic solvent. In this case, this deposit is made preferablyafter that of the noble metal(s) of the platinum group and roasting ofthe solid, followed if required by reduction with hydrogen at hightemperature, for example between 300 and 500° C. The organometalliccompounds are chosen in the group constituted by the complexes of saidpromoter metal, in particular the polyketone complexes and thehydrocarbylmetals such as the alkyl, cycloalkyl, aryl, alkylaryl andarylalkyl metals. Organohalogen compounds can also be used. One can citein particular tin tetrabutyl in the case where the promoter metal istin, lead tetraethyl in the case where the promoter metal is lead andindium triphenyl in the case where the promoter metal is indium. Theimpregnation solvent can be chosen from the group constituted by theparaffinic, naphthenic or aromatic hydrocarbons containing from 6 to 12carbon atoms per molecule and the halogen organic compounds containing 1to 12 atoms of carbon per molecule. One can cite for example, n-heptane,methylcyclohexane and chloroform. Mixtures of the solvents defined abovecan also be used.

The halogen, for example chlorine, can be introduced into the catalystat the same time as another metallic constituent, for example in thecases where a halide is used as precursor compound of the metal of theplatinum group, of the promoter metal or of the alkali or alkaline-earthmetal. This introduction can also be carried out through impregnation ofthe support by means of an aqueous solution containing an acid or ahalided salt. For example, chlorine can be deposited by using a solutionof hydrochloric acid. Chlorine can also be introduced by roasting of thecatalyst at a temperature between for example 400 and 900° C., in thepresence of an organic compound containing the halogen, such as forexample CCl₄, CH₂ Cl₂ and CH₃ Cl.

Of course, at least two constituents of the catalyst can be introducedsimultaneously, for example beginning from a solution containing theirprecursor compounds. The constituents can also be introducedsuccessively in any order whatsoever, from separate solutions. In thislatter case, one can proceed with intermediary drying and/or roasting.

The formation of the alumina matrix can be carried out using state ofthe art techniques for formation of catalysts such as, for example,extrusion, drip coagulation, coating, drying by atomization orpelletizing.

In the preferred embodiment, the preparation process is characterized inthat it comprises the following successive stages:

a) formation of the matrix of γ alumina or η alumina or of a mixture ofγ alumina and η alumina,

b) deposit of silicon on this matrix,

c) possible deposit of at least one doping metal, and

d) simultaneous or successive deposit

of at least one promoter metal chosen from among tin, germanium, indium,gallium, thallium, antimony, lead, rhenium, manganese, chromium,molybdenum and tungsten;

of at least one element chosen from the group constituted by fluorine,chlorine, bromine, iodine, and

of at least one noble metal of the platinum group.

After formation of the matrix and deposit of all the constituents, onecan proceed to a final thermal treatment between 300 and 1000° C., whichcan comprise only a single stage preferably at a temperature between 400and 900° C., and in an atmosphere containing oxygen, preferably in thepresence of free oxygen or air. This treatment generally corresponds todrying-roasting following the deposit of the last constituent. Afterformation of the matrix and deposit of all the constituents, thecomplementary hydrothermal treatment is carried out, at a temperaturebetween 300 and 1000° C. and preferably 400 to 700° C., in a gaseousatmosphere containing steam and if required a halogen such as chlorine.

This treatment can be carried out on a bed crossed by a current of gasor in a static atmosphere. Preferably, the gaseous atmosphere containswater and if required at least one halogen. The molar content in wateris from 0.05 to 100%, preferably 1 to 50%. The molar content of halogenis 0 to 20%, and preferably between 0 and 10%, and preferably againbetween 0 and 2%. The length of time of this treatment is variabledepending on the conditions of temperature, partial water pressure andquantity of catalyst. Advantageously this value is between one minuteand 30 hours, preferably between 1 and 10 hours. The gaseous atmosphereused is for example based on air, oxygen, or an inert gas such as argonor nitrogen.

The role of this high-temperature treatment in the presence of water isimportant. As described in the examples given below, in the presence ofsilicon which preserves the matrix in alumina(s) from a loss of sspecific surface area during the different regenerating treatments, inan unexpected fashion, severe thermal treatment in the presence of waterapplied to this type of catalyst has the effect of preserving it from aloss of specific surface area, while still improving the catalyticperformance.

After the final thermal treatment, the catalyst can be submitted to anactivation treatment under hydrogen at high temperature, for example ata temperature between 300 and 550° C.

The process for treatment under hydrogen consists for example of raisingthe temperature slowly in a current of hydrogen until the maximumreduction temperature is reached, generally between 300 and 550° C. andpreferably between 350 and 450° C., followed by maintenance at thistemperature for a period which generally lasts between 1 and 6 hours.

According to the invention, the catalyst described above is used forreactions for the conversion of hydrocarbons, and more particularly inthe processes of reforming gasolines and production of aromatics.

The reforming processes make it possible to raise the octane number ofthe gasoline fractions from the distillation of crude oil and/or otherrefining processes.

The processes for production of aromatics provide the bases (benzene,toluene and xylene) which can be used in petrochemistry. These processeshave a supplementary interest in that they contribute to the productionof large quantities of hydrogen which is indispensable for thehydrotreatment processes of the refinery.

These two processes differ through the choice of operating conditionsand the composition of the load.

The typical load treated by these processes contains paraffinic,naphthenic and aromatic hydrocarbons containing 5 to 12 atoms of carbonper molecule. This load is defined, among other things, by its densityand its composition by weight.

In order to activate these processes, the hydrocarbon load is put intocontact with the catalyst of the present invention under the appropriateconditions, for example at a temperature of 400 to 700° C., at apressure ranging from atmospheric pressure to 4 Mpa, using either themobile bed or fixed bed technique. When the fixed bed technique is used,the pressure is between 1 and 2 MPa, and when the mobile bed techniqueis used, the pressure is preferably from 0.1 to 0.9 MPa.

Generally contact is made with a mass debit of load treated per unitmass of catalyst and per hour between 0.1 and 10 kg/kg.hr.

A part of the hydrogen produced is recycled according to a molarrecycling content of between 0.1 and 8. This content is the molarrelation of the debit of hydrogen recycled over the mass flow of theload.

Other features and advantages of the invention will become clearer whenreading the examples which follow, it being understood that the datagiven are illustrative and non-restrictive.

EXAMPLE 1

This example illustrates the production of a catalyst comprising amatrix formed of a mixture of γ alumina and η alumina, on which aredeposited silicon, chlorine, tin and platinum.

a) Formation of the Matrix in Alumina

First of all the matrix is prepared in alumina by mixing a powder of γalumina of a specific surface area of 220 m² /gm and a powder of ηalumina with a specific surface area equal to 320 m² /gm which has beenprepared by roasting bayerite. The proportion of η alumina is 10% byweight. This mixture is then formed by extrusion, then roasted in acurrent of dry air at 520° C. for 3 hours.

b) Deposit of Silicon

After cooling down, silicon is deposited on the roasted matrix byputting it into contact with an ethanolic solution of tetraethylorthosilicate (Si(OC₂ H₅)₄. The concentration of this solution is 18.5gm of silicon per liter. This contact is made at ambient temperaturewith stirring, for 2 hours. The solvent is then evaporated under reducedpressure. Then the impregnated extrusions are dried at 120° C. for 15hours, and roasted at 530° C. in a current of dry air for 2 hours. Onethus obtains a support conforming to the invention.

c) Deposit of Platinum, Tin and Chlorine

Next platinum, tin and chlorine are deposited simultaneously on thesupport by impregnation with an aqueous chlorinated solution containingper liter:

0.96 gm of tin under the form SnCl₂, and

0.81 gm of platinum under the form H₂ PtCl₆.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

d) Hydrothermal Treatment

A hydrothermal treatment is then carried out in the presence of waterand chlorine. With this aim, the catalyst is treated at 510° C. for 2hours in a current of 2000 dm³ /hr of air for 1 kg of solid product.This air contains water and chlorine injected in a preheating zonesituated upstream from the bed of solid. The molar concentrations inwater and chlorine are equal to 1% and 0.05% respectively.

The specifications of the catalyst obtained are given in table 1.

EXAMPLE 2

The same operating mode is followed as for example 1 in order to preparea catalyst comprising the same constituents, apart from the fact thatone does not carry out the hydrothermal treatment of stage d).

[ . . . ] The molar concentrations of water and chlorine arerespectively 1% and 0.05%.

The characteristics of the catalyst obtained are given in Table 1.

EXAMPLE 2

The same operating method as in example 1 is used to prepare a catalysthaving the same constituents, except that it does not include thehydrothermal treatment of stage d).

The characteristics of the catalyst obtained are also given in table 1.

Comparative Example 1

In this example, the same operating method as in example 1 is used, butduring stage a) only γ alumina is used, and silicon depositing stage a)and hydrothermal treatment stage d) are not carried out.

The characteristics of the catalyst obtained are also given in table 1.

                  TABLE 1                                                         ______________________________________                                              proportion                                                                             Specific                                                                              Platinum                                                                             Tin   Chlorine                                                                             Silicon                                  η alumina                                                                          surface content                                                                              content                                                                             content                                                                              content                                  (weight %                                                                              area    (weight                                                                              (weight                                                                             (weight                                                                              (weight                            Catalyst                                                                            of matrix)                                                                             (m.sup.2 /g)                                                                          %)     %)    %)     %)                                 ______________________________________                                        Ex. 2 10       227     0.25   0.17  1.08   1.04                               Ex. 1 10       228     0.24   0.18  1.13   1.02                               Com-  0        219     0.23   0.18  1.15   0                                  parat.                                                                        Ex. 1                                                                         ______________________________________                                    

EXAMPLE 3

In this example, the catalysts of examples 1 and 2 and of thecomparative example are tested [ . . . ]

    ______________________________________                                        content of naphthenes                                                                              33.1% by weight                                          content of aromatics 12.1% by weight                                          ______________________________________                                    

The following operating conditions are used:

    ______________________________________                                        temperature         500° C.                                            total pressure      1.0 Mpa                                                   mass flow of the load                                                                             1.8 kg/kg of catalyst                                     length of time      100 hr.                                                   ______________________________________                                    

At the end of the functioning period, the deactivated catalyst isregenerated through controlled combustion of the coke and adjustment ofits chlorine content to around 1.10% by weight. The specific surfacearea of the support is measured after this regeneration. Then afteractivation of the catalyst at high temperature by hydrogen, the load isinjected for a new functioning period. Thus, each catalyst has beensubmitted to 5 cycles of operation-regeneration. The specific surfaceareas corresponding to the beginning of the first and last cycles andthe performances obtained after 15 hours of operation for each of thesetwo cycles are recorded in table 2 below.

                  TABLE 2                                                         ______________________________________                                                                      Desired                                                        Specific                                                                              Reformate                                                                            octane                                                                              Aromatic                                                                             C4                                                surface yield  rating                                                                              yield  yield                                             area    (weight                                                                              (weight                                                                             (weight                                                                              (weight                            Catalyst                                                                              Cycle  (m.sup.2 /g)                                                                          %)     %)    %)     %)                                 ______________________________________                                        Example 1      227     91.2   97.4  67.7   5.2                                2       5      226     91.5   96.9  66.8   5.1                                Example 1      228     91.4   98.0  68.3   5.2                                1       5      225     91.9   97.2  67.2   4.3                                Comparat.                                                                             1      219     90.3   97.2  67.0   5.9                                Example 5      197     91.7   94.8  64.8   5.1                                1       Example 2                                                             ______________________________________                                    

If the performances of the catalysts in examples 1 and 2 are compared tothose of the catalyst of the prior art (comparative example 1), it isfound that the catalysts of examples 1 and 2 give the best yields inaromatics and the best reformate octane ratings. It is also found thatthese gains are achieved without affecting reformate yields.

If consideration is now given to the development over 5 cycles, itbecomes apparent that the drop in specific surface areas of examples 1and 2 is much lower than that of the catalyst in the prior art.

This smaller drop is concomitant with better maintained yields ofaromatics and octane ratings.

With the catalysts of the invention it is therefore possible to obtainbetter octane ratings with unchanged reformate yields that are stablethroughout several cycles. cycles, better octane numbers for unchangedyields of reformed product.

EXAMPLE 4

This example illustrates the production of a s catalyst comprising amatrix formed of a mixture of γ alumina and η alumina, on which aredeposited silicon, chlorine, potassium, rhenium and platinum.

a) Formation of the Matrix in Alumina

First of all the alumina matrix is prepared by mechanical mixing of apowder of γ alumina of specific surface area of 220 m² /gm and a powderof η alumina of specific surface area equal to 320 m² /gm which has beenprepared by roasting bayerite. The η alumina proportion is 30% byweight. This mixture is then formed by extrusion, and roasted in acurrent of dry air at 520° C. for 3 hours.

b) Deposit of Silicon

After cooling down, silicon is deposited on the roasted matrix byputting it into contact with an ethanolic solution of tetraethylorthosilicate Si(OC₂ H₅)₄. The concentration of this solution is 2.5 gmof silicon per liter. This contact is made at ambient temperature withstirring, for 2 hours. The solvent is then evaporated under reducedpressure. Then the impregnated extrusions are dried at 120° C. for 15hours, and roasted at 530° C. in a current of dry air for 2 hours.

c) Potassium Deposit

Then the extrusions are put into contact with an aqueous solution ofpotassium carbonate K₂ CO₃ containing 12.8 gm/l of potassium. Thiscontact is carried out at ambient temperature for 1 hour, and then theimpregnated matrix is dried at 120° C. over 15 hours and roasted at 530°C. in a current of dry air for 2 hours.

d) Deposit of Platinum and Chlorine

The platinum and part of the chlorine are then deposited simultaneouslyon this support through impregnation by a chlorinated aqueous solutioncontaining per liter:

8.20 gm of chlorine in the form of HCl, and

1.00 gm of platinum in the form of H₂ PtCl₆.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

e) Deposit of Rhenium and Chlorine

Then the rhenium and the rest of the chlorine are depositedsimultaneously through impregnation by a chlorinated aqueous solutioncontaining per liter:

4.20 gm of chlorine in the form of HCl, and

1.50 gm of rhenium in the form of ReCl₃.

After drying, the impregnated support is roasted at 530° C. for 2 hoursin a current of dry air.

f) Hydrothermal Treatment

A hydrothermal treatment is then carried out in the presence of waterand chlorine. For this, the catalyst is treated at 510° C. for 2 hoursin a current of air of 2000 dm³ /hr for 1 kg of solid product. This aircontains water and chlorine injected in a preheating zone situatedupstream from the bed of solid. The molar concentrations in water andchlorine are equal to 1% and 0.05% respectively.

The specifications of the catalyst obtained are given in table 3.

EXAMPLE 5

The same operating mode is followed as in example 4 to prepare acatalyst comprising the same constituents, apart from the fact that instage c), the impregnation solution contains 6.4 gm/l of potassium, andthe hydrothermal treatment of stage e) is not carried out.

The specifications of the catalyst obtained are also given in table 3.

Comparative Example 2

In this example, the same operating mode as in example 4 is followed,but in stage a) only γ alumina is used, and stages b) and c) fordepositing silicon and potassium and stage f) for hydrothermal treatmentare not applied.

The specifications of the catalyst obtained are also given in table 3.

EXAMPLE 6

This example illustrates the production of a catalyst comprising amatrix formed from a mixture of γ alumina and η alumina comprising 8% ηalumina, on which are deposited silicon, chlorine, potassium, tin andplatinum.

For this preparation, the same operating mode as in example 4 isfollowed, utilizing in stage a) 8% by weight of η alumina and instead ofstages d) and e) carrying out a single simultaneous deposit stage ofplatinum, tin and chlorine through impregnation with a chlorinatedaqueous solution containing per liter:

0.81 gm of platinum in the form H₂ PtCl₆, and

0.96 gm of tin in the form SnCl₂.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

A hydrothermal treatment is then carried out in the presence of waterand chlorine as in stage f) of example 4.

The specifications of the catalyst obtained are given in table 3.

EXAMPLE 7

The same operating mode as in example 6 is then followed to prepare acatalyst comprising the same constituents, apart from the fact that instage c), the impregnation solution contains 6.4 gm/l of potassium, andthe final hydrothermal treatment in the presence of water and chlorineis not carried out.

The specifications of the catalyst obtained are also given in table 3.

Comparative Example 3

In this example, the same operating mode as in example 6 is followed butin stage a) only γ alumina is used, and stages b) and c) for depositingsilicon and potassium and the last stage f) for hydrothermal treatmentin the presence of water and chlorine as described in example 1 are notapplied.

The specifications of the catalyst obtained are also given in table 3.

                                      TABLE 3                                     __________________________________________________________________________        Propor-                                                                            Speci-                                                                   tion fic Plati-                Potas-                                         η alumina                                                                      sur-                                                                              num Tin Rhenium                                                                            Chlorine                                                                           Silicon                                                                           sium                                           (weight                                                                            face                                                                              content                                                                           content                                                                           content                                                                            content                                                                            content                                                                           content                                    Cata-                                                                             of   area                                                                              (weight                                                                           (weight                                                                           (weight                                                                            (weight                                                                            (weight                                                                           (weight                                    lyst                                                                              matrix)                                                                            (m.sup.2 /gm)                                                                     %)  %)  %)   %)   %)  %)                                         __________________________________________________________________________    Exam-                                                                             30   237 0.25                                                                              0   0.47 1.17 0.045                                                                             0.23                                       ple 4                                                                         Exam-                                                                             30   238 0.24                                                                              0   0.50 1.07 0.045                                                                             0.12                                       ple 5                                                                         Compa                                                                             0    216 0.23                                                                              0   0.48 1.12 0   0                                          Exam-                                                                         ple 2                                                                         Exam-                                                                             8    227 0.22                                                                              0.18                                                                              0    1.14 0.13                                                                              0.76                                       ple 6                                                                         Exam-                                                                             8    225 0.25                                                                              0.16                                                                              0    1.06 0.15                                                                              0.34                                       ple 7                                                                         Compa                                                                             0    219 0.23                                                                              0.18                                                                              0    1.15 0   0                                          r.                                                                            Examp                                                                         le 3                                                                          __________________________________________________________________________

EXAMPLE 8

In this example, the catalysts of examples 4 and 5 and the comparativeexample 2 are tested, for conversion of a load of hydrocarbons with thefollowing specifications:

    ______________________________________                                        volume mass at 20° C.                                                                       0.742 kg/dm.sup.3                                        octane number required                                                                             ˜41                                                content of paraffins 52.2% by weight                                          content of naphthenes                                                                              32.4% by weight                                          content of aromatics 15.4% by weight                                          ______________________________________                                    

The following operating conditions are used:

    ______________________________________                                        temperature         500° C.                                            total pressure      1.5 Mpa                                                   mass flow of the load                                                                             2.0 kg/kg of catalyst                                                         and per hr.                                               length of time      100 hr.                                                   ______________________________________                                    

The performances of the catalysts are recorded in table 4 below, and areexpressed in yields by weight and of the octane number required of thereformed product.

                  TABLE 4                                                         ______________________________________                                                 Reformate                                                                              Hydrogen Aromatics                                                                            C4                                                   yield    yield    yield  yield                                                (weight  (weight  (weight                                                                              (weight                                                                             C4                                    Catalyst %)       %)       %)     %)    aromatics                             ______________________________________                                        Example 4                                                                              85.1     3.2      60.2   11.7  0.19                                  Example 5                                                                              84.7     3.3      60.8   12.0  0.20                                  Comparative                                                                            83.9     3.0      60.0   13.1  0.22                                  example 2                                                                     ______________________________________                                    

If a comparison is made between the performances of the catalysts ofexample 4 and the comparative example 2 on the one hand, and those ofthe catalysts of example 5 and of the comparative example 2 on theother, it is noted that the catalysts of examples 4 and 5 haveperformances which are a clear improvement over the prior art catalyst(comparative example 2).

In fact, the yields of light cracking products C4 obtained during thetest of the two catalysts of examples 4 and 5 are very significantlylower than those observed for the catalyst of the comparative example 2.

Thus, it can be seen that the relation between the yields of crackingproducts C4 and the yields of aromatic compounds, called C4-/aromaticsin the table above, is lower for the two catalysts according to theinvention. The selectivity of the catalysts vis-a-vis the aromaticproducts required become higher as this relation becomes lower.

The catalysts of examples 4 and 5 containing, in addition compared tothe catalyst of example 2, η alumina, silicon and potassium, presentimproved specifications relative to the catalyst of comparative example2, notably as far as weaker selectivity of cracking products isconcerned, and thus improved selectivity for aromatic products.

EXAMPLE 9

In this example, the catalysts of examples 6 and 7 and the comparativeexample 3, are tested for conversion of a load of hydrocarbons with thefollowing specifications:

    ______________________________________                                        volume mass at 20° C.                                                                       0.736 kg/dm.sup.3                                        octane number required                                                                             ˜38                                                content of paraffins 54.8% by weight                                          content of naphthenes                                                                              33.1% by weight                                          content of aromatics 12.1% by weight                                          ______________________________________                                    

The following operating conditions are used:

    ______________________________________                                        temperature         495° C.                                            total pressure      0.75 Mpa                                                  mass flow of the load                                                                             1.8 kg/kg of catalyst                                     length of time      100 hr.                                                   ______________________________________                                    

At the end of the functioning period, the deactivated catalyst isregenerated through controlled combustion of the coke and adjustment ofits chlorine content to around 1.10% by weight. The specific surfacearea of the support is measured after this regeneration. Then afteractivation of the catalyst at high temperature by hydrogen, the load isinjected for a new functioning period. Thus, each catalyst has beensubmitted to 5 cycles of operation-regeneration. The specific surfaceareas corresponding to the beginning of the first and last cycles andthe performance obtained after 15 hours of operation for each of thesetwo cycles are recorded in table S below.

                  TABLE 5                                                         ______________________________________                                                       Specific                                                                              Reformate    Aromatics                                                                            C4                                                surface yield  Octane                                                                              yield  yield                                             area    (weight                                                                              number                                                                              (weight                                                                              (weight                            Catalyst                                                                              cycle  (m.sup.2 /gm)                                                                         %)     required                                                                            %)     %)                                 ______________________________________                                        Example 1      227     91.2   97.9  68.2   5.5                                6       5      220     92.1   96.8  67.3   4.7                                Example 1      225     91.2   97.6  67.9   5.4                                7       5      213     91.5   96.5  66.5   5.3                                Compara-                                                                              1      219     90.7   97.5  67.2   6.0                                tive    5      198     91.6   95.4  65.1   5.2                                Example                                                                       ______________________________________                                    

If a comparison is made between the performances of the catalysts ofexamples 6 and 7, with those of the prior art catalyst (comparativeexample 3), it can be seen that the catalysts of examples 6 and 7present better yields in aromatics and better octane numbers for thereformed product. It can also be noted that these improvements areachieved without the reformed product yields being affected.

If the evolution over 5 cycles is now considered, it can be seen thatthe fall in the specific surface areas of examples 6 and 7 is much lessthan that of the prior art catalyst. This smaller fall is accompanied bybetter maintenance of yields in aromatics and octane numbers.

EXAMPLE 10

This example illustrates the production of a catalyst comprising amatrix formed of a mixture of γ alumina and η alumina, on which aredeposited silicon, chlorine, lanthanum, rhenium and platinum.

a) Formation of the Matrix in Alumina

First of all the alumina matrix is prepared by mechanical mixing of apowder of γ alumina of specific surface area 220 m² /gm and a powder ofη alumina of specific surface area equal to 320 m² /gm which has beenprepared by roasting bayerite. The proportion of η alumina is 40% byweight. This mixture is then formed by extrusion, and then roasted in acurrent of dry air at 520° C. for 3 hours.

b) Deposit of Silicon

After cooling down, silicon is deposited on the roasted matrix byputting it into contact with an ethanolic solution of tetraethylorthosilicate Si(OC₂ H₅)₄. The concentration of this solution is 2.5 gmof silicon per liter. This contact is made at ambient temperature withstirring, for 2 hours. The solvent is then evaporated under reducedpressure. Then the impregnated extrusions are dried at 120° C. for 15hours, and roasted at 530° C. in a current of dry air for 2 hours.

c) Lanthanum Deposit

Then the extrusions are put into contact with an aqueous solution oflanthanum nitrate La(NO₃)₃, 6H₂ O containing 42 gm/l of lanthanum. Thiscontact is carried out at ambient temperature for 2 hours, and then theimpregnated matrix is dried at 120° C. for 15 hours and roasted at 530°C. in a current of dry air for 2 hours.

d) Deposit of Platinum and Chlorine

Then the platinum and part of the chlorine are deposited simultaneouslyon this support through impregnation by a chlorinated aqueous solutioncontaining per liter.

8.20 gm of chlorine in the form of HCl, and

1.00 gm of platinum in the form of H₂ PtCl₆.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

e) Deposit of Rhenium and Chlorine

Then the rhenium and the rest of the chlorine are depositedsimultaneously through impregnation by a chlorinated aqueous solutioncontaining per liter:

4.20 gm of chlorine in the form of HCl, and

1.50 gm of rhenium in the form of ReCl₃.

After drying, the impregnated support is roasted at 530° C. for 2 hoursin a current of dry air.

f) Hydrothermal Treatment

A hydrothermal treatment is then carried out in the presence of waterand chlorine. For this, the catalyst is treated at 510° C. for 2 hoursin a current of air of 2000 dm³ /hr for 1 kg of solid product. This aircontains water and chlorine injected in a preheating zone situatedupstream from the bed of solid. The molar concentrations in water andchlorine are equal to 1% and 0.05% respectively.

The specifications of the catalyst obtained are given in table 6.

EXAMPLE 11

The same operating mode is followed as for example 10 to prepare acatalyst comprising the same constituents, except that in stage c), theimpregnation solution contains 21 gm/l of lanthanum, and thehydrothermal-treatment of stage f) is not applied.

The specifications of the catalyst obtained are also given in table 6.

EXAMPLE 12

This example illustrates the production of a catalyst comprising amatrix formed of γ alumina, on which are deposited silicon, chlorine,lanthanum, rhenium and platinum.

For this preparation, the same operating mode as for example 10 isfollowed, but stage f) is not applied. In stage a) only γ alumina isused and stage b) is carried out in the same conditions as those ofexample 10, except for the concentration in silicon of the solution,which is 3.2 gm/l. Stages c), d) and e), are carried out as in example10.

The specifications of the catalyst obtained are given in table 6.

EXAMPLE 13

The same operating mode as for example 12 is followed to prepare acatalyst comprising the same constituents, but one additionalhydrothermal treatment is applied in the same conditions as those inexample 10 (stage f)

The chlorine content of the catalyst is 1.08% by weight.

Comparative Example 4

In this example, the same operating mode as for example 10 is followed,but in stage a) only γ alumina is used and stages b) and c) fordepositing silicon and lanthanum and stage f) for hydrothermal treatmentare not applied.

The specifications of the catalyst obtained are also given in table 6.

EXAMPLE 14

This example illustrates the production of a catalyst comprising amatrix formed from a mixture of γ alumina and η alumina comprising 12% ηalumina, on which are deposited silicon, chlorine, lanthanum, tin andplatinum.

For this preparation, the same operating mode as in example 10 isfollowed, utilizing in stage a) 12% by weight of η alumina and insteadof stages d) and e) carrying out a single simultaneous deposit stage ofplatinum, tin and chlorine through impregnation with a chlorinatedaqueous solution containing per liter:

0.81 gm of platinum in the form H₂ PtCl₆, and

0.969 gm of tin in the form SnCl₂.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

A hydrothermal treatment is then carried out in the presence of waterand chlorine as in stage f) of example 10, but operating at 500° C. withmolar concentrations in water and chlorine respectively of 1.5% and0.02%.

The specifications of the catalyst obtained are given in table 6.

EXAMPLE 15

The same operating mode as in example 14 is followed to prepare acatalyst comprising the same constituents, apart from the fact that instage c), the impregnation solution contains 21 gm/l of lanthanum, andthe final hydrothermal treatment of stage f) in the presence of waterand chlorine is not carried out.

The specifications of the catalyst obtained are also given in table 6.

Comparative Example 5

In this example, the same operating mode as in example 14 is followedbut in stage a) only γ alumina is used and one stages b) and c) fordepositing silicon and lanthanum and the last stage f) for hydrothermaltreatment in the presence of water and chlorine of example 14 are notused.

The specifications of the catalyst obtained are given in table 6.

                                      TABLE 6                                     __________________________________________________________________________                  Plati-                                                               Proportion                                                                         Specific                                                                          num Tin Rhenium                                                                            Chlorine                                                                           Silicon                                                                           Lanthanum                                      η alumina                                                                      surface                                                                           content                                                                           content                                                                           content                                                                            content                                                                            content                                                                           content                                   Cata-                                                                              (% weight                                                                          area                                                                              (weight                                                                           (weight                                                                           (weight                                                                            (weight                                                                            (weight                                                                           (weight                                   lyst of matrix)                                                                         (m.sup.2 /gm)                                                                     %)  %)  %)   %)   %)  %)                                        __________________________________________________________________________    Example                                                                            40       0.23                                                                              0   0.24 1.18 0.028                                                                             0.47                                      10                                                                            Example                                                                            40       0.22                                                                              0   0.24 1.09 0.028                                                                             0.11                                      11                                                                            Example                                                                            0        0.24    0.23 1.05 0.035                                                                             0.43                                      12                                                                            Compar.                                                                            0        0.23                                                                              0   0.25 1.12 0   0                                         Example                                                                       Example                                                                            12   229 0.24                                                                              0.16                                                                              0    1.13 0.11                                                                              1.70                                      14                                                                            Example                                                                            12   231 0.24                                                                              0.16                                                                              0    1.08 0.13                                                                              0.82                                      15                                                                            Compar.                                                                            0    219 0.25                                                                              0.18                                                                              0    1.15 0   0                                         Example                                                                       5                                                                             __________________________________________________________________________

EXAMPLE 16

In this example, the catalysts of examples 10 and 13 and the comparativeexample 4 are tested, for conversion of a load of hydrocarbons with thefollowing specifications:

    ______________________________________                                        volume mass at 20° C.                                                                       0.742 kg/dm.sup.3                                        octane number required                                                                             ˜41                                                content of paraffins 52.2% by weight                                          content of naphthenes                                                                              32.4% by weight                                          content of aromatics 15.4% by weight                                          ______________________________________                                    

The following operating conditions are used:

    ______________________________________                                        temperature         490° C.                                            total pressure      1.4 Mpa                                                   mass flow of the load                                                                             3.0 kg/kg of catalyst                                     by mass             and per hr.                                               ______________________________________                                    

The performances of the catalysts are recorded in table 7 below, and areexpressed in yields by weight and of the octane number required of thereformed product.

                  TABLE 7                                                         ______________________________________                                                 Reformate                                                                              Hydrogen Aromatics                                                                            C4                                                   yield    yield    yield  yield                                                (% by    (% by    (% by  (% by C4                                    Catalyst weight)  weight)  weight)                                                                              weight)                                                                             aromatics                             ______________________________________                                        Example 10                                                                             86.0     3.2      58.9   10.8  0.18                                  Example 11                                                                             85.2     3.2      59.2   11.6  0.20                                  Example 12                                                                             84.8     3.1      58.7   12.1  0.20                                  Example 13                                                                             85.7     3.2      58.8   11.1  0.19                                  Comparative                                                                            84.4     3.0      58.4   12.6  0.22                                  example 4                                                                     ______________________________________                                    

If a comparison is made between the performances of the catalysts ofexample 10 and the comparative example 4 on the one hand, and those ofthe catalysts of example 11 and of the comparative example 4 on theother, it is noted that the catalysts of examples 10 and 11 haveperformances which are a clear improvement over the catalyst of priorart (comparative example 4).

In fact, the yields of light cracking products C4 obtained during thetest of the two catalysts of examples 10 and 11 are very significantlylower than those observed for the catalyst of the comparative example 4.

Thus, it can be seen that the relation between the yields of crackingproducts C4 and the yields of aromatic compounds, called C4-/aromaticsin the table above, is lower for the two catalysts according to theinvention. The selectivity of the catalysts vis-a-vis the aromaticproducts required will become higher as this relation is lowered.

The catalysts of examples 10 and 11 containing, in addition compared tothe catalyst of comparative example 4, η alumina, silicon and lanthanum,present improved specifications relative to the catalyst of comparativeexample 4, notably as far as weaker selectivity of cracking products isconcerned, and thus improved selectivity for aromatic products.

If a comparison is made between the performances of the catalysts ofexamples 12 and 13, it can be noted that the catalyst of example 13presents improved performance compared with the catalyst of example 12.

In fact, the catalyst of example 13 presents a yield in crackingproducts C4- which is clearly lower and a yield in aromatics which isevidently higher,. The relation between yields in cracking products C4-and the yields of aromatic compounds, called C4-/aromatics in the tableabove, is lower for the catalyst of example 13. The selectivity of thecatalysts vis-a-vis the aromatic products required will become higher asthis relation is lowered.

The catalysts of examples 12 and 13 contain, among others, silicon andlanthanum. The catalyst of example 13 has, in addition, been submittedto a is hydrothermal treatment. It presents improved specificationsrelative to the catalyst of example 12, notably as far as weakerselectivity of cracking products is concerned, and thus improvedselectivity for aromatic products.

EXAMPLE 17

In this example, the catalysts of examples 14 and 15 and the comparativeexample 5 are tested, for conversion of a load of hydrocarbons with thefollowing specifications:

    ______________________________________                                        volume mass at 20° C.                                                                       0.736 kg/dm.sup.3                                        octane number required                                                                             ˜38                                                content of paraffins 54.8% by weight                                          content of naphthenes                                                                              33.1% by weight                                          content of aromatics 12.1% by weight                                          ______________________________________                                    

The following operating conditions are used:

    ______________________________________                                        temperature         500° C.                                            total pressure      0.40 Mpa                                                  mass flow of the load                                                                             2.0 kg/kg of catalyst                                     length of time      100 hr.                                                   ______________________________________                                    

At the end of the functioning period, the deactivated catalyst isregenerated through controlled combustion of the coke and adjustment ofits chlorine content to around 1.10% by weight. The specific surfacearea of the support is measured after this regeneration. Then afteractivation of the catalyst at high temperature by hydrogen, the load isinjected for a new functioning period. Thus, each catalyst has beensubmitted to 5 cycles of operation-regeneration. The specific surfaceareas corresponding to the beginning of the first and last cycles andthe performances obtained after 15 hours of functioning for each ofthese two cycles are recorded in table 8 below.

                  TABLE 8                                                         ______________________________________                                                       Specific                                                                              Reformate    Aromatics                                                                            C4                                                surface yield  Octane                                                                              yield  yield                                             area    (% by  number                                                                              (% by  (% by                              Catalyst                                                                              cycle  (m.sup.2 /gm)                                                                         weight)                                                                              required                                                                            weight)                                                                              weight)                            ______________________________________                                        Example 1      229     90.0   101.0 71.7   6.5                                14      5      224     90.8   100.1 71.1   5.7                                Example 1      231     89.2   101.4 71.8   7.2                                15      5      222     90.2   100.3 70.8   6.4                                Compara-                                                                              1      219     88.2   100.9 70.5   8.5                                tive    5      194     89.4   98.6  67.8   7.5                                Example 5                                                                     ______________________________________                                    

If a comparison is made between the performances of the catalysts ofexamples 14 and 15, and those of the prior art catalyst (comparativeexample 5), it can be seen that the catalysts of examples 14 and 15present better yields in aromatics and better octane numbers for thereformed product. It can also be noted that these improvements areachieved without the reformed product yields being affected.

If the evolution over 5 cycles is now considered, it can be seen thatthe fall in the specific surface areas of examples 14 and 15 is muchless than that of the prior art catalyst. This smaller fall isaccompanied by better maintenance of yields in aromatics and octanenumbers.

EXAMPLE 18

This example illustrates the production of a catalyst comprising amatrix formed of a mixture of γ alumina and η alumina, on which aredeposited silicon, chlorine, zirconium, rhenium and platinum.

a) Formation of the Matrix in Alumina

First of all the alumina matrix is prepared by mechanical mixing of apowder of γ alumina of specific surface area 220 m² /gm and a powder ofη alumina of specific surface area equal to 320 m² /gm which has beenprepared by roasting bayerite. The proportion of η alumina is 20% byweight. This mixture is then formed by extrusion, and then roasted in acurrent of dry air at 520° C. for 3 hours.

b) Deposit of Silicon

After cooling down, silicon is deposited on the roasted matrix byputting it into contact with an ethanolic solution of tetraethylorthosilicate Si(OC₂ H₅)₄. The concentration of this solution is 2.5 gmof silicon per liter. This contact is made at ambient temperature withstirring, for 2 hours. The solvent is then evaporated under reducedpressure. Then the impregnated extrusions are dried at 120° C. for 15hours, and roasted at 530° C. in a current of dry air for 2 hours.

c) Zirconium Deposit

Then the extrusions are put into contact with an aqueous solution ofzirconyl chloride ZrOCl₂, 8H₂ O containing 26.7 gm/l of zirconium. Thiscontact is carried out at ambient temperature for 2 hours, and then theimpregnated matrix is dried at 120° C. for 15 hours and roasted at 530°C. in a current of dry air for 2 hours.

d) Deposit of Platinum and Chlorine

Then the platinum and part of the chlorine are deposited simultaneouslyon this support through impregnation by a chlorinated aqueous solutioncontaining per liter:

8.20 gm of chlorine in the form of HCl, and

1.00 gm of platinum in the form of H₂ PtCl₆.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

e) Deposit of Rhenium and Chlorine

Then the rhenium and the rest of the chlorine are depositedsimultaneously through impregnation by a chlorinated aqueous solutioncontaining per liter:

4.20 gm of chlorine in the form of HCl, and

b 1.50 gm of rhenium in the form of ReCl₃.

After drying, the impregnated support is roasted at 530° C. for 2 hoursin a current of dry air.

f) Hydrothermal Treatment

A hydrothermal treatment is then carried out in the presence of waterand chlorine. For this, the catalyst is treated at 510° C. for 2 hoursin a current of 2000 dm³ /hr of air for 1 kg of solid product. This aircontains water and chlorine injected in a preheating zone situatedupstream from the bed of solid. The molar concentrations in water andchlorine are equal to 1% and 0.05% respectively.

The specifications of the catalyst obtained are given in table 9.

EXAMPLE 19

The same operating mode is followed as for example 18 to prepare acatalyst comprising the same constituents, except that in stage c), theimpregnation solution contains 13.3 gm/l of zirconium, and thehydrothermal treatment of stage f) is not applied.

The specifications of the catalyst obtained are also given in table 9.

Comparative Example 6

In this example, the same operating mode as in example 18 is followed,but in stage a) only γ alumina is used, and one stages b) and c) fordeposits of silicon and zirconium and stage f) for hydrothermaltreatment are not applied.

The specifications of the catalyst obtained are also given in table 9.

EXAMPLE 20

This example illustrates the production of a catalyst comprising amatrix formed of a mixture of γ alumina and η alumina, comprising 8% ofη alumina, on which are deposited silicon, chlorine, zirconium, tin andplatinum.

For this preparation, the same operating mode as for example 18 isfollowed, using in stage a) 8% by weight of η alumina and instead ofstages d) and e) carrying out a single stage of simultaneous deposit ofplatinum, tin, and chlorine through impregnation with a chlorinatedaqueous solution containing per liter:

0.81 gm of platinum in the form H₂ PtCl₆, and

0.96 gm of tin in the form SnCl₂.

The solution is left in contact with the support for 2 hours. Aftercentrifugation and drying for 4 hours at 120° C., the impregnatedsupport is roasted at 530° C. for 3 hours in a current of dry air.

A hydrothermal treatment in the presence of water and chlorine as instage f) of example 18 is then carried out.

The specifications of the catalyst obtained are given in table 9.

EXAMPLE 21

The same operating mode as for example 20 is followed, to prepare acatalyst comprising the same constituents, but in stage c), theimpregnation solution contains 13.3 gm/l of zirconium, and the finalhydrothermal treatment in the presence of water and chlorine is notcarried out.

The specifications of the catalyst obtained are also given in table 9.

Comparative Example 7

In this example, the same operating mode as for example 20 is followed,but in stage a) only γ alumina is used and stages b) and c) fordepositing silicon and zirconium and the last stage f) for hydrothermaltreatment in the presence of water and chlorine are not applied.

The specifications of the catalyst obtained are also given in table 9.

                                      TABLE 9                                     __________________________________________________________________________                  Plati-                Zirco-                                         Proportion                                                                         Specific                                                                          num Tin Rhenium                                                                            Chlorine                                                                           Silicon                                                                           nium                                           η alumina                                                                      surface                                                                           content                                                                           content                                                                           content                                                                            content                                                                            content                                                                           content                                   Cata-                                                                              (% weight                                                                          area                                                                              (weight                                                                           (weight                                                                           (weight                                                                            (weight                                                                            (weight                                                                           (% by                                     lyst of matrix)                                                                         (m.sup.2 /gm)                                                                     %)  %)  %)   %)   %)  weight)                                   __________________________________________________________________________    Example                                                                            20       0.24                                                                              0   0.26 1.16 0.032                                                                             0.51                                      18                                                                            Example                                                                            20       0.23                                                                              0   0.23 1.05 0.032                                                                             0.15                                      19                                                                            Compar.                                                                            0        0.23                                                                              0   0.25 1.12 0   0                                         Example                                                                       Example                                                                            8    223 0.22                                                                              0.17                                                                              0    1.12 0.12                                                                              1.72                                      20                                                                            Example                                                                            8    226 0.25                                                                              0.15                                                                              0    1.05 0.14                                                                              0.85                                      21                                                                            Compar.                                                                            0    219 0.24                                                                              0.18                                                                              0    1.15 0   0                                         Example                                                                       7                                                                             __________________________________________________________________________

EXAMPLE 22

In this example, the catalysts of examples 18 and 19 and the comparativeexample 6 are tested, for conversion of a load of hydrocarbons with thefollowing specifications:

    ______________________________________                                        volume mass at 20° C.                                                                       0.742 kg/dm.sup.3                                        octane number required                                                                             ˜41                                                content of paraffins 52.2% by weight                                          content of naphthenes                                                                              32.4% by weight                                          content of aromatics 15.4% by weight                                          ______________________________________                                    

The following operating conditions are used:

    ______________________________________                                        temperature          505° C.                                           total pressure       1.3 Mpa                                                  mass flow of the load                                                                              4.0 kg/kg of catalyst                                                         and per hr.                                              length of time       100 hr.                                                  ______________________________________                                    

The performances of the catalysts are recorded in table 10 below, andare expressed in yields by weight and of the octane number required ofthe reformed product.

                  TABLE 10                                                        ______________________________________                                                 Reformate                                                                              Hydrogen Aromatics                                                                            C4                                                   yield    yield    yield  yield                                                (% by    (% by    (% by  (% by C4                                    Catalyst weight)  weight)  weight)                                                                              weight)                                                                             aromatics                             ______________________________________                                        Example 18                                                                             86.0     3.2      60.4   10.8  0.18                                  Example 19                                                                             85.2     3.2      61.1   11.5  0.19                                  Comparative                                                                            84.4     3.0      59.8   12.8  0.21                                  example 6                                                                     ______________________________________                                    

If a comparison is made between the performances of the catalysts ofexample 18 and the comparative example 6 on the one hand, and those ofthe catalysts of example 19 and of the comparative example 6 on theother, it is noted that the catalysts of examples 18 and 19 haveperformances which are a clear improvement over the catalyst of priorart (comparative example 6).

In fact, the yields of light cracking products C4 obtained during thetest of the two catalysts of examples 18 and 19 are very significantlylower than those observed for the catalyst of the comparative example 6.

Thus, it can be seen that the relation between the yields of crackingproducts C4 and the yields of aromatic compounds, called C4-/aromaticsin the table above, is lower for the two catalysts of examples 18 and19. The selectivity of the catalysts vis-a-vis the aromatic productsrequired will become higher as this relation is lowered.

The catalysts of examples 18 and 19 containing, in addition to thecatalyst of comparative example 6, η alumina, silicon and zirconium,present improved specifications relative to the catalyst of comparativeexample 6, notably as far as weaker selectivity of cracking products isconcerned, and thus improved selectivity for aromatic products.

EXAMPLE 23

In this example, the catalysts of examples 20 and 21 and the comparativeexample 7 are tested, for conversion of a load of hydrocarbons with thefollowing specifications:

    ______________________________________                                        volume mass at 20° C.                                                                       0.742 kg/dm.sup.3                                        octane number required                                                                             ˜41                                                content of paraffins 44.2% by weight                                          content of naphthenes                                                                              39.4% by weight                                          content of aromatics 16.4% by weight                                          ______________________________________                                    

The following operating conditions are used:

    ______________________________________                                        temperature         505° C.                                            total pressure      0.75 Mpa                                                  mass flow of the load                                                                             2.5 kg/kg of catalyst                                     length of time      100 hr.                                                   ______________________________________                                    

At the end of the functioning period, the deactivated catalyst isregenerated through controlled combustion of the coke and adjustment ofits chlorine content to around 1.10% by weight. The specific surfacearea of the support is measured after this regeneration. Then afteractivation of the catalyst at high temperature by hydrogen, the load isinjected for a new functioning period. Thus, each catalyst has beensubmitted to 5 cycles of operation-regeneration. The specific surfaceareas corresponding to the beginning of the first and last cycles andthe performances obtained after 15 hours of functioning for each ofthese two cycles are recorded in table 11 below.

                  TABLE 11                                                        ______________________________________                                                       Specific                                                                              Reformate    Aromatics                                                                            C4                                                surface yield  Octane                                                                              yield  yield                                             area    (% by  number                                                                              (% by  (% by                              Catalyst                                                                              cycle  (m.sup.2 /gm)                                                                         weight)                                                                              required                                                                            weight)                                                                              weight)                            ______________________________________                                        Example 1      223     89.7   102.1 73.3   6.6                                20      5      212     90.7   100.7 71.9   5.8                                Example 1      226     90.4   101.9 73.6   5.9                                21      5      209     90.7   100.5 71.6   5.7                                Comparative                                                                           1      219     89.2   102.0 72.8   7.3                                Example 7                                                                             5      196     90.2   100.2 70.7   6.4                                ______________________________________                                    

If a comparison is made between the performances of the catalysts ofexamples 20 and 21, and those of the prior art catalyst (comparativeexample 7), it can be seen that the catalysts of examples 20 and 21present better yields in aromatics and better octane numbers for thereformed product. It can also be noted that these improvements areachieved without the reformed product yields being affected.

If the evolution over 5 cycles is now considered, it can be seen thatthe fall in the specific surface areas of examples 20 and 21 is muchless than that of the prior art catalyst. This smaller fall isaccompanied by better maintenance of yields in aromatics and octanenumbers.

The process of the invention thus makes it possible to improve in asubstantial way the results obtained by the conversion of hydrocarbonsinto aromatic components, in terms of selectivity and stability duringthe reaction cycles.

We claim:
 1. A process for the conversion of hydrocarbons into aromaticcompounds, comprising contacting a composition comprising hydrocarbonswith a catalyst under temperature and pressure conditions to producesaid aromatic compounds, wherein the catalyst comprises:a matrixcontaining 0 to 100% by weight of η transition alumina, and theremaining weight percentage of the matrix, up to 100%, consisting of γtransition alumina, and, relative to the total weight of the catalyst:from 0.01 to 2% by weight of silicon, from 0.1 to 15% by weight of atleast one halogen selected from the group consisting of fluorine,chlorine, bromine and iodine, from 0.01 to 2% by weight of at least onenoble metal selected from the platinum group, and from 0.005 to 10% byweight of at least one promoter metal selected from the group consistingof tin, germanium, indium, gallium, thallium, antimony, lead, rhenium,manganese, chromium, molybdenum and tungsten, said catalyst having beenpreviously treated hydrothermally at a temperature of 300 to 1000° C. ina gaseous atmosphere containing steam, wherein the water molar contentof the gaseous atmosphere is at least 0.05%.
 2. The process inaccordance with claim 1, wherein the matrix contains from 3 to 70% byweight of the η transition alumina.
 3. The process in accordance withclaim 1, wherein the catalyst further comprises, relative to the totalweight of the catalyst, from 0.001 to 8% by weight of at least onedoping metal selected from the group consisting of the alkali metals andthe alkaline-earth metals.
 4. The process in accordance with claim 3,wherein the doping metal is potassium.
 5. The process in accordance withclaim 1, wherein the catalyst further comprises, relative to the totalweight of the catalyst, from 0.001 to 10% by weight of at least onedoping metal selected from the group consisting of titanium, zirconium,hafnium, cobalt, nickel and zinc.
 6. The process in accordance withclaim 5, wherein the doping metal is zirconium.
 7. The process inaccordance with claim 1, wherein the catalyst further comprises,relative to the total weight of the catalyst, from 0.001 to 10% byweight of at least one doping metal selected from the lanthanide series.8. The process in accordance with claim 7, wherein the doping metal islanthanum.
 9. The process in accordance with claim 1, wherein thesilicon content of the catalyst is from 0.01 to 1% by weight.
 10. Theprocess in accordance with claim 1, wherein the halogen content of thecatalyst is from 0.2 to 10% by weight.
 11. The process in accordancewith claim 1, wherein the total noble metal content of the catalyst isbetween 0.1 and 0.8% by weight.
 12. The process in accordance with claim1, wherein the promoter metal is selected from the group consisting ofrhenium, manganese, chromium, molybdenum, tungsten, indium and thallium.13. The process in accordance with claim 12, wherein the promoter metalis rhenium.
 14. The process in accordance with claim 1, wherein thepromoter metal is selected from the group consisting of tin, germanium,indium, antimony, lead, thallium and gallium.
 15. The process inaccordance with claim 14, wherein the promoter metal is tin.
 16. Theprocess in accordance with claim 1, wherein the halogen is chlorine. 17.The process in accordance with claim 1, wherein the noble metal isplatinum.
 18. The process in accordance with claim 1, wherein thehydrothermal treatment is conducted for a period of 1 minute to 30 hoursin a gaseous atmosphere having a water molar content between 0.05 and100%.
 19. The process in accordance with claim 1, wherein the watermolar content is between 1 and 50%.
 20. The process in accordance withclaim 1, wherein the period of hydrothermal treatment is from 1 to 10hours.
 21. The process in accordance with claim 1, wherein the gaseousatmosphere further comprises at least one halogen.
 22. The process inaccordance with claim 21, wherein the halogen content of the gaseousatmosphere is at most 20% in mol.
 23. The process in accordance withclaim 21, wherein the halogen content of the gaseous atmosphere is atmost 10% in mol.
 24. The process in accordance with claim 21, whereinthe halogen content of the gaseous atmosphere is at most 2% in mol. 25.The process in accordance with claim 1, wherein the gaseous atmosphereis air, oxygen, argon or nitrogen.
 26. The process in accordance withclaim 1, wherein said hydrocarbons comprise paraffin, naphthenic andaromatic hydrocarbons having from 5 to 12 carbon atoms, and arecontacted with the catalyst at a temperature of 400 to 700° C. under apressure ranging from atmospheric pressure to 4 MPa.
 27. The process inaccordance with claim 12, wherein the pressure ranges from 0.1 to 0.9MPa.
 28. The process in accordance with claim 14, wherein the pressureranges from 0.1 to 0.9 MPa.
 29. The process in accordance with claim 26,wherein the hydrocarbons are contacted with the catalyst under a massflow of composition ranging from 0.1 to 10 kg of hydrocarbons per kg ofcatalyst per hour.
 30. The process in accordance with claim 1, whereinthe conversion of said hydrocarbons to said aromatic compounds is acatalytic reforming operation.
 31. The process in accordance with claim1, wherein said matrix contains from 0.1 to 99% by weight of ηtransition alumina, and the remaining weight percentage of the matrix,up to 100% consisting of γ transition alumina.